If adult Still's disease (ASD) can sometimes lead to severe destructive joint lesions and to various systemic manifestations, life-threatening complications are very rare. However, a long-term and high-dose corticosteroid therapy is often required to control the disease, with frequent corticodependence. Some authors have proposed methotrexate as a second line drug for ASD, that could permit a corticosteroid sparing effect. We report two cases of acute fatal infectious complications--legionella pneumonitis and multiple brain abscess caused by Nocardia asteroides--in two patients treated for ASD with both corticosteroids and methotrexate. These two cases raise the problem of the immunodepression induced by this combination therapy and point out the difficulties in aggressive forms of ASD.